Modern aircraft may operate over a wide range of temperatures from Saharan heat to arctic cold, from high temperatures at low altitudes to subzero temperatures at high altitudes. Aircraft engines require a constant fuel flow at a given speed over those temperature ranges to ensure efficient, safe operation. For instance, for some applications, fuel flow should have no more than a .+-.2% weight flow deviation at a constant engine speed over a temperature range from -51.degree. to 66.degree. C. Variations in fuel flow, as effected by temperature, can cause a fuel/air mixture for an engine to be too lean or too rich. This improper fuel/air mixture can cause engine surging or flameout endangering the engine and the aircraft.
It is known in the art to provide a pack having a series of orifices within a fuel line to meter the fuel flow to an engine. Fuel pressure is controlled upstream and downstream of the pack and a pressure differential therebetween induces a desired amount of fuel to flow through the pack. Each orifice within the pack has a common length (L) and a common diameter (D), and is angularly offset from each adjacent orifice. This prior art pack provides a relatively constant weight flow over only a very narrow temperature range, which may not comport with the ambient conditions encountered by modern aircraft.
Accordingly what is needed in the art is an orifice pack that maintains a relatively constant fuel flow at a given engine speed and over a wide temperature range. Proper fuel flow to the engine over the temperature range ensures safe engine and aircraft operation.